Effects of FiO2 adjustment on hyperoxia biomarkers and postoperative complications using oxygen reserve index during
Buğra Aykenar1, Asude Ayhan2, Sinan Issı3
1Department of Intensive Care, Faculty of Medicine, Gazi University, Mevlana street, Ankara, 06560, Türkiye. aykenar.bugra@gazi.edu.tr.
Background:
One-lung ventilation (OLV) is commonly used in thoracic surgery but increases the risk of intraoperative hypoxemia. To prevent hypoxia, high fractions of inspired oxygen (FiO₂) are frequently administered; however, excessive oxygen exposure may lead to hyperoxia and oxidative tissue injury. The Oxygen Reserve Index (ORi) is a non-invasive monitoring parameter that provides real-time information on moderate hyperoxia. This study aimed to evaluate whether ORi-guided oxygen titration reduces intraoperative FiO₂ exposure and influences oxidative stress biomarkers and postoperative outcomes in patients undergoing OLV.
Methods:
In this prospective, randomized controlled trial, 60 patients undergoing elective thoracic surgery requiring OLV were allocated to either an ORi-guided group or a conventional oxygen management group. In the ORi group, FiO₂ was adjusted according to predefined ORi thresholds, whereas in the control group oxygen management was guided solely by pulse oximetry. The primary outcome was the mean intraoperative FiO₂ administered during OLV and throughout the entire surgery. Secondary outcomes included serum and tracheal aspirate levels of interleukin-6 (IL-6), superoxide dismutase (SOD), and malondialdehyde (MDA), postoperative pulmonary complications, and surgical site infections.
Results:
Mean intraoperative FiO₂ was significantly lower in the ORi group compared with the control group during OLV and across total surgery duration (p < 0.001). Oxygen saturation and ventilatory parameters were comparable between groups. Biomarker levels showed significant time-dependent changes; however, no significant differences were observed between groups, and no significant group × time interaction was detected. The incidence of postoperative pulmonary complications and surgical site infections did not differ between groups.
Conclusions:
ORi-guided oxygen titration during OLV enables safe reduction of intraoperative FiO₂ while maintaining adequate oxygenation. Although this strategy did not translate into measurable differences in oxidative stress biomarkers or postoperative complications, these findings provide important clinical evidence regarding the physiological impact of moderate hyperoxia in thoracic surgery.
Trial Registration:
ClinicalTrials.gov identifier NCT07359833. First submission date: 17.01.2026 Retrospectively registered on 21.1.2026.
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